1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor laser element having a ridge part.
In the invention, a “lamination layer” means a layer to be laminated to form a semiconductor laser element, a “width direction” is used synonymously with a direction perpendicular to a laminating direction in which lamination layers are laminated and an extending direction of the ridge part. A “widthwise length” is used synonymously with a length in width direction.
2. Description of the Related Art
A semiconductor laser element is used as a light source for reading and writing information from and on an optical recording medium. For instance, a red semiconductor laser element is used for optical pickup to read and write information from and to a digital versatile disc (DVD). A higher laser beam output is desired to the semiconductor laser element being thus used as the light source in order to realize a higher writing speed on the optical recording medium. It is also desired that the semiconductor laser element be provided with a high temperature operating performance which allows the semiconductor laser element to operate even in an environment at high temperature brought by an increasing output of the laser beams.
FIG. 9 is a cross sectional view showing a semiconductor laser element 1 of a first related art. A semiconductor laser element 1 realizes the increasing output of the laser beams and a high temperature operating performance. A method of manufacturing the semiconductor laser element 1 will be described below. An n-type substrate 2, an n-type cladding layer 3, an active layer 4, a p-type cladding layer 5, an intermediate layer 6, and a p-type capping layer 7 are sequentially laminated in a laminating direction. A stripe-shaped ridge part 8 is formed by etching a part of the p-type capping layer 7, the intermediate layer 6, and the p-type cladding layer 5 from one side in the laminating direction by use of a wet etching. A compound semiconductor structure 9 having the ridge part 8 is thus formed. A dielectric film 10 is laminated so as to coat a remaining part of the compound semiconductor structure not involving a surface part of the ridge part 8, which faces the laminating direction, and then a p-type electrode 11 is disposed. Further, an n-type electrode 12 is disposed so as to coat the compound semiconductor structure. Thus manufactured is the semiconductor laser element 1 which realizes the increase of the output laser beams and the high temperature operating performance (for instance, refer to Japanese Unexamined Patent Publication JP-A 2003-347674 (pages 3 to 5 and FIG. 2)).
FIG. 10 is a cross sectional view showing a semiconductor laser element 13 of a second related art. Similarly to the semiconductor laser element 1 of the first related art, the semiconductor laser 13 comprises: a compound semiconductor structure 15 having a ridge part 14; an n-type current block layer 17 laminated on a p-type cladding layer 16 so as to coat a remaining part not involving a surface part of the ridge part 14, which faces the laminating direction; a p-type electrode 18 formed on one side in a laminating direction; and an n-type electrode 19 formed on the other side in a laminating direction. In the ridge part 14 of the semiconductor laser element 13, an intermediate layer 20 and a p-type capping layer 21 are formed so as to protrude in a form of window roof in a width direction. The ridge part 14 is thus provided with a window roof part 22 which protrudes in the width direction (for instance, refer to Japanese Unexamined Patent Publication JP-A 2003-069154 (FIG. 4)).
FIG. 11 is a cross sectional view showing the semiconductor laser element 1 of the first related art in a state of having a void inside thereof. In the semiconductor laser element 1 of the first related art, the ridge part 8 is formed by the wet etching. This makes it impossible to form a uniform width of the ridge part as shown in FIG. 9. In practice, as shown in FIG. 11, the intermediate 6 and the p-type capping layer 7 protrude in the width direction so that a window roof part 23 which protrudes in the width direction is formed. When the dielectric layer 10 and an electrode are disposed in a state where the window roof 23 is thus formed, the window roof 23 prevents the dielectric layer 10 and the p-type electrode 11 from being laminated in a region on the other side of the window roof part 23 in a laminating direction so that the dielectric layer 10 and the p-type electrode 11 cannot be disposed so as to have desired layer thicknesses. In addition, due to a variation of the layer thickness, a void 24 is formed between the dielectric layer 10 and the p-type electrode 11. Such variation of the layer thickness and a layer discontinuity by the void formed between the layers incur variation of an element's characteristic of the semiconductor laser element 1. Furthermore, a heat radiation characteristic is largely lowered by forming the void 24 inside the semiconductor laser element 1. This makes the semiconductor laser element 1 be forced to operate at high temperature. Therefore, a large thermal stress acts on the semiconductor laser element 1 and a crystal defect occurs. As a result, there arise troubles such as an increase of operating current and an occurrence of kink.
In the semiconductor laser element 13 of the second related art, the window roof part 22 is formed on the ridge part 14 and therefore, there arises troubles such as the increase of operating current and the occurrence of kink which are similar to the troubles of the semiconductor laser element of the first related art. The applicant has been trying to prevent the element's characteristic from deteriorating by adjusting a width of the window roof part, but the void is still not prevented from occurring. Consequently, by merely adjusting the width of the window roof part 22 of the semiconductor laser element 13, the heat radiation characteristic cannot be prevented from deteriorating and it is difficult to improve the operating performance at high temperature.